Media: Issue with webp image support on old atomic site

[aerych]

While testing webp image support I happened to use an atomic site created on 2020-02-27. On this particular site .webp images failed to upload, both in the app and in a browser. However, on a newly/recently created atomic site .webp images were supported as expected.

This behavior suggests older atomic sites could be configured differently compared to present day, and we may see other issues with .webp on older sites.

Opening this issue to track.